Marine navigation devices often include a display that shows a map of at least a portion of a body of water in the vicinity of the current geolocation of a marine vessel with which the marine navigation device is being utilized. The map may include a representation of the terrain or soil at the bottom of the water. Marine navigation devices display contour lines associated with depths of a plurality of geographic areas associated with a body of water. The displayed contour lines are presented in a higher density for areas associated with, large gradients or slopes of the underwater terrain, while flatter underwater regions result in a lower contour line density. Conventional marine navigation devices may remove an entire contour line to reduce the density of contour lines presented on a display.